' ' T-IA THE 

PURIFICATION OF SEWAGE 


BY FORCED AERATION. 



REPORT 

of an Experimental Investigation of the Value of a Process 
for Purifying Sewage by Means of Artificially 
Aerated Bacterial Filters. 


BY 


GEO. E. WARING, Jr., M. Inst. C. E. 





























THE 


PURIFICATION OF SEWAGE 
BY FORCED AERATION. 


REPORT 

of an Experimental Investigation of the Value of a Process 
for Purifying Sewage by Means of Artificially 
Aerated Bacterial Filters. 


GEO. E. WARING, Jr., M. Inst. C. E. 



NEWPORT, R. I. 

F. W. MARSHALL, PRINTER. 

1895. 









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The Purification of Sewage by Forced Aeration. 


A STUDY OF THE RESULTS OF ARTIFICIALLY STIMULATING BACTERIAL 
ACTION IN SEWAGE. 


We are accustomed to think of all things material as divided 
into three great kingdoms — Animal, Vegetable and Mineral. 
Viewed superficially, these divisions seem clearly defined and, 
at least to a great extent, permanent. The truth is that matter 
is constantly passing from one division to another, and that in 
none of them, save the mineral, is any stability to be found. 
Certain elements have never been discovered in organic form, 
but all vegetable structures are built of materials borrowed from 
the mineral- world, which must, sooner or later, be returned to 
it. All animal tissues are drawn from the vegetable, directly 
or indirectly, and, in due time, back to the dust must they go. 

Until about 1890 the theories concerning the destruction of 
waste organic matters were in a state of speculation and develop¬ 
ment, but much positive knowledge on the subject has been 
gained within the last five years. 

Foremost in importance are the results of the experiments 
made by the Massachusetts State Board of Health at its station 
at Lawrence. The detailed records of these experiments and 
the deductions of the eminent scientists in charge of them, as 
published in the Reports of the Board, constitute the most valu¬ 
able addition yet made to sanitary science. It is sufficient, for 
the purposes of this paper, to say that these experiments prove 
beyond question the fact that organic matter in sewage is re¬ 
duced to its original mineral elements — absolutely destroyed as 
organic matter — by the action of living organisms; and that 
they clearly indicate — if not the precise manner in which the 
work is done—at least the conditions which favor or retard its 
accomplishment. The experiments consisted in passing sewage 




4 


THE PURIFICATION OF SEWAGE 


at intervals through tanks filled with various filtering materials. 
The simplest and most striking illustration of the process was 
obtained in the use of two tanks, one filled with gravel-stones 
none of which were less than one-eighth of an inch nor more 
than three-eighths of an inch in diameter, and the other filled with 
stones varying from three-quarters to one and a quarter inches 
in diameter. In both cases the material was carefully washed, 
that no sand or soil might remain attached to it. Concerning 
the results obtained from these tanks, Mr. Hiram F. Mills, who 
was then in charge of the station, says: 

“The experiments with gravel-stones give us the best il¬ 
lustration of the essential character of intermittent filtration of 
sewage. In these, without straining the sewage sufficiently to 
remove even the coarser suspended particles, the slow movement 
of the liquid in thin films over the surface of the stones, with 
air in contact, caused to be removed for some months 97 per 
cent, of the organic nitrogenous matter, a large part of which 
was in solution, as well as 99 per cent, of the bacteria, which 
were, of course, in suspension, and enabled these organic mat¬ 
ters to be oxidized or burned, so that there remained in the ef¬ 
fluent but three per cent, of the decomposable organic matter 
of the sewage, the remainder being converted into harmless 
mineral matter. 

“The mechanical separation of any part of the sewage by 
straining through sand is but an incident, which, under some 
conditions, favorably modifies the result; but the essential con¬ 
ditions are very slow motion of very thin films of liquid over 
the surface of particles having spaces between them sufficient 
to allow air to be continually in contact with the films of liquid. 

“With these conditions, it is essential that certain bacteria 
should be present to aid in the process of nitrification. These, 
we have found, come in the sewage at all times of the year, 
and the conditions just mentioned appear to be most favorable for 
their efficient action, and at the same time most destructive to 
them and to all kinds of bacteria that are in sewage.” 

We see, therefore, that the process that is called “filtration ” 
is not filtration, but a mere exposure of the sewage, in the pres¬ 
ence of air, to the action of destructive bacteria, which, so far 
as known, are the only agents that can oxidize and destroy the 
organic impurities of sewage. The presence of air (oxygen) is 


BY FORCED AERATION. 


5 


absolutely essential to the inoffensive decomposition of organic 
wastes. In its absence certain forms of putrefaction and disin¬ 
tegration will be set up, but such processes are offensive and, 
to the best of our knowledge, they are usually dangerous. When 
sewage is delivered into porous, open-jointed absorption drains, 
laid in surface soil, it soaks away into ground which is suffi¬ 
ciently permeated with air to induce bacterial oxidation. When 
sewage is spread over the surface of the ground, the process of 
destruction is essentially the same, but exposure to the air is 
more complete and oxidation is, at proper temperatures, propor¬ 
tionately more active. In each of these cases, however, as well as 
in the case'of the filters at Lawrence, described above, complete 
and inoffensive purification is obtained only by the intermittent 
application of sewage. The liquid applied must be allowed to 
drain away and be followed in its descent through the interstices 
of the soil by the air necessary to facilitate the bacterial destruc¬ 
tion of the impurities adhering to its particles. 

The experiments herein described, in the treatment of sew¬ 
age in artificially aerated filters, were undertaken with a full 
understanding of the facts stated above, and after a careful study 
of the researches of the Massachusetts Board of Health. They 
illustrate no new theory; they deal with no purifying process but 
the natural one of bacterial oxidation, which has been in con¬ 
stant operation since the first appearance of life upon the earth. 
Their aim has been to find a way of artificially producing con¬ 
ditions more favorable to natural bacterial action than can be 
found under ordinary circumstances. 

The process consists in the mechanical straining out of all 
solid matters carried in suspension in sewage, and their subse¬ 
quent destruction by forced aeration, and the purification of the 
clarified sewage by bacterial oxidation of its dissolved organic 
matters in an artificially aerated filter. 

The results accomplished in the experiments herein described 
exceeded the most sanguine expectations. Sewage, loaded with 
grease, dirt, excreta, and the putrid overflow of cesspools, es¬ 
caped from the tanks clear, white, and limpid. The impurities 
were not passed through in disguise, the foul smell was not 
masked by other odors; the effluent water was actually clean,— 
a good drinking water. 

This complete regeneration continued through five months, 


6 


THE PURIFICATION OF SEWAGE 


and when the filters by which it had been performed were taken 
apart, they too were clean. The filth had not accumulated in 
them; it had completely disappeared. 

The process is not only valuable as an economical and effi¬ 
cient means of purifying sewage. It is equally applicable to the 
cleansing of liquid wastes from slaughter houses, glue factories, 
fertilizer factories, garbage disposal works, silk and woolen mills, 
—in short, it will purify all water that has been soiled by or¬ 
ganic matter. 

Described briefly, the apparatus and the mode of operation 
are as follows:— 

The sewage, after passing through suitable screens, which 
withhold large solids, such as rags, paper, lemon-rinds, etc., flows 
slowly, horizontally, through or over a shallow bed (say 6 inches 
deep) of coarse broken stone or similar material, which serves 
to catch and retain the coarser floating particles which have es¬ 
caped the screens. 

These broken-stone beds should be provided in triplicate, 
each to have ample capacity to receive the entire flow for a cer¬ 
tain period; and they are to be used in alternation, allowing 
to each twice as much time for rest and recuperation as for 
active service. When one of these areas is thrown out of use, 
it is drained and its accumulation of filth is exposed to the 
action of air, which results in its speedy destruction, leaving 
the bed in condition again to receive its quota of sewage when 
its turn comes. 

Leaving this area of broken stone, the sewage, freed from 
its coarser solids, passes to a straining tank filled with fine brok¬ 
en stone, coarse gravel, locomotive cinders, coke, or similar po¬ 
rous material. This tank is divided into two compartments by 
a diaphragm, which extends nearly to the bottom of the tank. 
The sewage passes down through one of these compartments, 
flows under the diaphragm and rises through the other com¬ 
partment, overflowing at its top. The rate of flow through the 
tank must be sufficiently slow to allow the deposition upon the 
surfaces of the filtering medium of the solid particles suspended 
in the sewage. If the speed be properly regulated, practi¬ 
cally all of the suspended impurities are retained in this tank, 
and the sewage leaves it as a slightly opalescent but clear 
liquid, with a perceptible odor. At this stage it compares 


BY FORCED AERATION. 


7 


favorably with the effluent of chemical precipitation works. 

When one of these straining tanks has been in operation 
for a considerable time, the accumulation of sludge at the sur¬ 
face of the filtering material clogs the pores of the filter and 
decreases its capacity, although the quality of the effluent is in 
no wise impaired. When this condition is reached, the flow is 
turned to another tank of similar construction, where the strain¬ 
ing process begins anew. The filter tank which has just been 
thrown out of use is drained, and an abundant supply of air, 
under light pressure, is forced by a blower into the bottom of 
the tank (where means for its even distribution are provided), 
rising through the filtering medium in a strong current which 
penetrates into all its voids and pores. Under these conditions, 
rapid bacterial oxidation is set up and the retained impurities 
are speedily consumed, leaving the tank in a clean condition, 
ready for further use. 

It will probably be best to provide four of these straining 
tanks, to be used in alternation, allowing to each a period of 
aeration three times as long as its period of use. The filters 
which were in use at Newport during the whole time of the 
experiment (over five months) without any renewal of material, 
showed no signs of deterioration, but were practically as clean 
at its termination as when they were new, and were capable 
of producing as good results. 

The degree of purification attained at this stage of the pro¬ 
cess is, in many cases, sufficient to satisfy all requirements. When 
purification to a drinking-water standard is necessary, it may 
be obtained by further treatment, as follows: 

After passing the straining tanks, the sewage, which has 
been relieved of all matters in suspension, but which still contains 
nearly or quite all of the dissolved impurities originally in it, 
flows to an aerating tank. This is similar in construction to the 
straining tanks, save that it has no dividing diaphragm, the 
sewage passing in at the top and escaping, as purified water, 
through a trapped outlet at the bottom. It must also be con¬ 
siderably larger than the straining tanks, for the sewage, instead 
of passing through the filter in a solid column, as in the former 
case, trickles down in a thin film over the surfaces of the par¬ 
ticles of coke or other filtering material; while, through the 
voids between the particles, and in immediate contact with the 


8 


THE PURIFICATION OF SEWAGE 


trickling films of liquid, a current of air is constantly rising, 
being introduced at the bottom of the tank by a blower. 

After the filter has been a short time in use, the nitrifying 
organisms, which have entered with the sewage, develop, and, 
in the presence of abundant food supplied by the sewage, and 
abundant oxygen furnished by the blast, multiply with great 
rapidity, until their number has reached a point at which the 
average food supply is only capable of feeding the existing col¬ 
ony, and further multiplication is checked. When a sufficient 
colony of organisms has become established, the consumption 
of the organic matter in the liquid passing through the tank 
will be practically complete, so long as the quantity is reasona¬ 
bly uniform. Any sudden and marked increase or diminution 
in the rate of flow will make it necessary for the colony of or¬ 
ganisms to adapt itself to the new conditions, and this it will 
do, within reasonable limits, in a short time. 

As these nitrifying tanks are constantly aerated, they are 
used continuously , and one area, of sufficient size to care for the 
flow, is all that need be provided. 

The process by which the impurities of the sewage are re¬ 
moved is the purely natural one on which depends the ultimate 
destruction of all organic matter. When sewage is spread over 
the surface of the ground, as in irrigation, it is exposed to the 
atmosphere in thin broad sheets, and the bacteria which reduce 
its putrescible matters are active because air is abundant. The 
process in the aerating tank described above is essentially the 
same, but in this case the earth is massed in cubical form, and 
the atmosphere is made to pervade the mass, so that every con¬ 
ceivable plane within it presents—so far as bacterial activity is 
concerned—the conditions of a natural surface. 

The same is true with regard to the straining tanks. While 
the sewage is passing through them, the action is merely me¬ 
chanical sedimentation. When the liquid has been drained off 
and the aeration has begun, the process and the result are the 
same as they would be if the accumulated sludge were spread 
in extremely thin sheets over the surface of a large area of soil. 


The construction of the experimental plant at Newport was 
begun in April, 1894. By special permission of the authorities 



FIGURE 1 
































BY FORCED AERATION . 


9 


of the city, a building 14 feet square was erected upon city prop¬ 
erty on Briggs Wharf, directly over the main outlet sewer and 
enclosing one of its manholes. The sewer at this point is I ! in 
section, 5 feet wide and 5 feet deep and with a grade of 1 to 
2000. At the end of the wharf, 104 feet beyond the point se¬ 
lected, the sewer delivers into a large settling chamber, and 
from this an iron pipe, laid on the bottom of the inner harbor, 
leads beyond the breakwater and discharges into the main channel. 
A storm overflow in the settling chamber (a weir in the sea 
wall) allows the direct discharge of sewage into the inner har¬ 
bor at times when the flow is unusually large. This overflow 
is provided with low tide-gates, but very high tides sweep over 
these and flood the settling chamber with salt water. The city 
is sewered according to the combined system. The street inlets 
deliver into large catch-basins, which in dry weather are little 
better than cesspools. Many of the sewer connections are mere¬ 
ly overflows from old cesspools, receiving only liquid which 
is stale and putrid. The main sewer, which of necessity has very 
little fall, is a sewer of deposit, in which putrefaction is con¬ 
stantly going on. Because of these conditions, the sewage used 
in the experiments was often far from “fresh,” although the 
analyses showed it to be of normal composition and fair average 
strength. It contained practically no manufacturing wastes, 
although at times there was evidence of the presence of gas 
liquor. The invert of the sewer at the manhole covered by the 
experiment station was 1.05 feet above low tide. The average 
flow of the sewer at low tide, when the outlet was free, was 
about 9 inches deep, but at high tide the water was backed 
up until it was from 2 to 2\ feet deep, and the current either 
entirely checked or reversed. Exceptionally high tides, which 
entered the settling chamber through the storm overflow, in¬ 
vaded the sewer, so that at times the pump drew nothing but 
slightly fouled salt water, and the'work had to be suspended in 
consequence. This was partially remedied by placing a dam, 
about 28 inches high, in the sewer, but at times the salt water 
swept over this. 

Within the building, upon a platform built over the manhole, 
a 10-inch diaphragm pump was placed, with a 3-inch galvanized 


IO 


THE PURIFICATION OF SEWAGE 


iron suction running to within about 8 inches of the bottom of 
the sewer.* 

The mouth of this suction was open — full bore — so that 
a fair sample of the sewage,— solids as well as liquids, might 
be had. The large rubber flap-valves of the pump, although 
occasionally choked, passed solid substances well, and objects of 
considerable size,—dead rats, halves of lemon, pieces of shoe 
leather and towels, cabbage leaves, etc.,— were delivered on 
the screen. The capacity of the pump at full stroke was .81 
gallons, but its average throw during the experiment was about 
.28 gallons, and its average speed was 5 to 8 strokes per minute. 
It was driven by an offset crank-pin so attached to a face-plate 
on a shaft that the stroke could be made of any length from o 
to 4 inches. A revolution counter, attached to the connecting 
rod, recorded the number of strokes. A 3-inch galvanized iron 
force-main ran from the pump to the screen overhead, which 
will be described later. This pipe was tapped close to the pump 
and a pet-cock inserted, from which the samples of sewage for 
analysis were taken. 

A 28-inch exhaust fan, made by the Boston Blower Com¬ 
pany, furnished the means of aerating the tanks. It ran, during 
the experiment, at speeds varying from 1500 to 4800 revolutions 
per minute, and delivered into a 12-inch galvanized iron blast 
pipe, which distributed the air through branches to the tanks. 
A pressure gauge attached to this pipe indicated the air pres¬ 
sure in ounces and in inches (of water). 

Both pump and blower were driven, through suitable shaft¬ 
ing, by a 3 H. P. Edison electric motor, supplied with current 
from the Newport Illuminating Company’s station. But 1^ H. 
P. was needed for the work, and the current was reduced, first 
by a rheostat, which after a time burnt out one of its coils, and 
later by a lamp resistance of twelve 32- and eight 50-candle- 
power lamps, arranged in series of two. 

Figure 1 shows the arrangement of pump, counter, blower, 
air-guage, shafting and motor. 

A chemical laboratory was provided, -suitably equipped for 
the determination of free and albuminoid ammonias, consumed 


* Later, during the dry weather, this was lowered to within 3^ inches 
of the bottom. 




FIGURE 2 


















BY FORCED AERATION . 


11 

oxygen, dissolved oxygen, chlorine, etc., and for the recording 
of meteorological conditions. 

The screening apron, straining tanks, aerating tanks and 
effluent tank were located in a yard outside of the building, and 
their general arrangement is clearly shown in Figure 2. The 
force-main from the pump delivered near the top of the building, 
under the large air-pipe, and, by means of a loose elbow and 
short nipple, the flow could be turned at will to either side of 
a partition which divided into two sections (for alternate use) a 
shallow bed of coarse broken stone, supported on a trestle. The 
function of this bed was to catch and retain the coarser solids 
contained in the sewage, before passing it to the tanks below. 
Each of these sections contained 20 square feet (4x5) of stone 
8 inches deep. In practice it was found that this area was in¬ 
sufficient for convenient working. It was effective in that it 
retained practically all of the coarser matters, but they accumu¬ 
lated so rapidly that one section soon choked and the flow had 
to be turned upon the other. The impurities in the section 
thrown out of use disappeared rapidly in its interval of rest, 
but before its cleansing was complete the other section would 
be choked and in need of attention. For this reason it became 
necessary to wash out these beds from time to time, though 
their work was much lightened later by placing a wire screen 
of ^-inch mesh under the force-main delivery. Three of these 
sections should have been provided, and each should have been 
of twice the actual size. This would have allowed ample time 
for the exercise of their self-cleansing properties. 

At one time one of these sections was filled with fine broken 
stone (f to inch). Its performance in withholding matters in 
suspension was admirable, but it choked too quickly and became 
so filled with pasty sludge that its aeration and recuperation 
were very slow. Without doubt the best results would be ob¬ 
tained by constructing straining aprons of sufficient size and in 
triplicate, and grading the size of the stone so that the coarsest 
shall be nearest to the delivery of raw sewage and the smaller 
sizes near the outlet. 

From the straining apron, the sewage, freed of its coarser 
solids, but still containing much fine matter in suspension and 
all that it originally had in solution, passed to the straining 


12 


THE PURIFICATION OF SEWAGE 


tanks. Of these there were originally four (Nos. i,* 2, 3 and 
4), similar in construction, but filled with different materials. 
Each tank had a total capacity of about 985 gallons. The top 
of No. 1 was about 4 inches below the delivery of the straining 
apron, and each succeeding number was 6 inches lower than the 
one next before it, so that the tanks could be used in series if 
desired, the overflow of No. 1 delivering into No. 2, its overflow, 
in turn, passing to No. 3, and so on. The internal arrangement 
of one of these tanks is shown in Figure 3. A is a false bottom 



* Afterwards No. 1 A. 


FIG. 3 


G 


























BY FORCED AERATION. 


i3 


of plank, perforated with |-inch holes about 4 inches apart and 
supported a few inches from the bottom on cleats. B is a gal¬ 
vanized iron air-pipe, 6 inches in diameter, branching from the 
12-inch air main, and delivering through the false bottom into 
the open space below. C is a layer of coarse broken stone (1 
to 2\ inch) 6 inches thick. In tank No. 1, this material was 
used for filling the whole tank. D is a cylindrical, diaphragm, 
of hooped staves, resting upon the broken stone C, and dividing 
the surface of the tank into a circle and a ring of equal area. 
E is the material with which the main body of the tank,—in¬ 
side and outside of the diaphragm,—was filled. In No. 2 it 
was fine broken stone (-J to J inch); in No. 3, round pebbles, 
of diameters ranging from f to f inch; and in No. 4, coarse 
white gravel, of very uniform size, free from sand, each grain 
being about inch in diameter. Each of these four tanks was 
fitted with a drainage cock F near its bottom, and a hole bored 
through the bottom and closed with a wooden plug G provided 
means for the rapid and complete emptying of any tank when 
desired. In draining a tank at the close of a run, when it had 
accumulated its quota of sludge and was about to be aerated, 
the liquid was drawn off slowly through the cock, to prevent 
such disturbance of the sediment deposited upon the particles 
of the stone as a rapid flow would have caused. A smaller 
cock H was placed near the top of each tank, just below the 
overflow line, and from this samples were taken for analysis 
and examination. The partially strained sewage from the apron 
was delivered on the surface of one of these tanks in the circle 
enclosed by the diaphragm. It passed down through the cen¬ 
tral cylinder of filtering material and under the diaphragm, and 
rose again through the annular space outside of the diaphragm, 
•overflowing through a spout into a gutter* leading to the central 
circle of the next straining tank, when two or more of these 
tanks were used in series, or to the aerating tank, for further 
treatment. 

As has been stated, the function of these four “strainers” 
was mere mechanical sedimentation. The liquid flowed slowly 


* Short lengths of hose were used at first to conduct the flow from 
tank to tank, as shown in Figure 2. Shallow wooden gutters were after¬ 
wards found to be more convenient 



i4 


THE PURIFICATION OF SEWAGE 


through them and the suspended matters, which were more or 
less fibrous or gelatinous in their nature, attached themselves 
to the particles of the filter, the coarser of them being deposited 
near the surface of the central cylinder and the finer progress¬ 
ing further and further into the mass. Samples drawn from 
the drainage cocks at the bottom proved nearly as clear as those 
taken from the sampling cocks near the point of overflow, show¬ 
ing that practically all of the solid matters were deposited in 
the central core during the downward dow of the water, and 
that very little work remained to be done as the liquid rose in 
the outside ring. This was the case when the sewage was ap¬ 
plied at the maximum rate attained in the experiment, 8,950,194 
gallons per acre, the water moving through the tank at the rate 
of about 3 feet per hour. It is reasonable to suppose that the 
deposition of the suspended matters of sewage would be more 
rapid and complete when the liquid is slowly rising than when 
it is descending, and it is probable, therefore, that at least twice 
this maximum amount could be passed through a similar filter 
without materially impairing the quality of the effluent. The 
periods of operation of each filter would, of course, be shortened, 
but the power of recuperation would not be impaired. While 
these tanks were in operation, the contained liquid effectually 
trapped the air pipe P, but as soon as a tank was drained, its 
water seal was broken and air from the blower poured into the 
open space beneath the false bottom, and, the drainage cock 
having been closed, rose through the contents of the tank, its 
pressure ensuring a distribution throughout the whole mass. 
This abundant supply of oxygen stimulated into activity the 
germs of decomposition which lay dormant in the tank. They 
speedily attacked the stored organic matter and reduced it to 
its mineral constituents, part of it being rendered soluble and 
passing off in the next flow of liquid through the tank and part 
escaping in gaseous form into the atmosphere. The substance 
of the deposited matter was completely destroyed and the filter 
was restored to a clean condition, ready for further use. 

The original plan provided for the use of these strainers in 
series, the flow from the apron passing in succession through 
Nos. 1, 2, 3 and 4; or, as a possible alternative, their employ¬ 
ment in pairs, Nos. 1 and 3, for instance, being in operation 
while Nos. 2 and 4 were aerating. It was soon found, however, 


BY FORCED AERATION . 


i5 


that, in the use of four strainers in succession, the sewage was 
detained so long in the tanks that it began to putrefy, the 
effluent from the fourth tank and sometimes that from the third 
being worse than their respective affluents. Even when two 
tanks were run in series, the improvement caused by the second 
was not sufficient to justify its use, and, during the latter part 
of the experiment, the flow was passed through but one strainer. 

The comparative efficiencies of the various strainers are 
clearly shown in the tables accompanying the report of the 
chemical work. The results obtained in the use of No. 1 were 
excellent, but this tank was found somewhat more difficult to 
clean than the others, because the larger voids between the 
stones permitted the accumulation of sludge in larger masses, 
which were not so easily disintegrated by the action of the air 
as the more divided masses which gathered in the other tanks. 
The use of No. 1 as a strainer was therefore abandoned, and 
the tank was converted into an aerator, No. 1 A, as is described 
below. 


Suspended matter having been removed from the sewage, 
mechanically, in the strainers, to be afterwards destroyed by 
forced bacterial action, the clarified, but still foul, liquid was 
led to the aerating tank, shown in section in Figure 4. This 
tank was of the same size as the others, and was set 6 inches 
lower than strainer No. 4. It had a perforated false bottom, 
with an 8-inch air-pipe delivering into the space below it. On 
this bottom was placed 6 inches of coarse broken stone, which 
was packed at the top with smaller stone, so as to support firmly 
the finer filling material, which was clean white gravel, similar 
to that used in No. 4, and 3 feet 9 inches deep. On this was 
placed another 6 inches of coarse broken stone K, packed with 
finer stone at the top, and the whole was covered with 6 inches 
of fine beach sand Z. Two vent pipes MM, made of single 
lengths of round 4-inch agricultural tile, pierced the covering 
of sand and communicated with the upper layer of broken stone 
beneath it. This tank had no diaphragm. The effluent from 
the strainer entered at its top, trickled down over the broken 
stone and gravel and ran out at the bottom through the pipe 
R, which discharged into an upright length of vitrified pipe S, 


i6 


THE PURIFICATION OF SEWAGE 


closed at one end, effectually trapping the outlet and preventing 
air from escaping with the effluent. This trap overflowed into 
a rectangular wooden tank of about 350 gallons capacity, sunk 
in the ground, which collected the effluent and allowed conven¬ 



ient inspection of it in bulk, giving a better general idea of the 
transparency and whiteness of the water than the laboratory 
samples or the turbidity-testing apparatus. 


wm/m/mm 

















































BY FORCED AERATION. 


i7 


In tank No. 5 the forced aeration was constant. Air was 
delivered at its bottom, and, being- prevented by the trap from 
passing out with the water, rose through the gravel to the upper 
layer of broken stone, and thence escaped, by means of the vent 
pipes, to the outer air. At times the discharge through these 
vents was sufficiently strong to carry with it good sized pieces 
of the broken stone in which their lower ends were embedded. 
At other times the current was scarcely perceptible. The liquid 
which was constantly trickling down in thin films over the sur¬ 
faces of the broken stone and gravel was always in immediate 
contact with a current of fresh air passing in an opposite direc¬ 
tion through the voids between the particles of stone. When 
the sewage was first applied, it sank through the layer of sand 
within a few inches of the point at which it was delivered and 
passed quickly through the tank, showing little or no improve¬ 
ment as it escaped. Gradually, however, the surface of the sand 
became partially clogged and the sewage was distributed over 
a wider area, until at length the whole surface of the tank 
was covered with liquid 2 or 3 inches deep. This secured uni¬ 
formity of distribution throughout the tank. Gradually, also, 
the organisms of nitrification began to multiply and to seize 
upon the dissolved impurities, destroying their organic character 
and transforming them into nitrites and nitrates, in which un¬ 
objectionable mineral form they escaped with the effluent. The 
first signs of this action were shown on June 12th. Once started, 
it increased rapidly, and by June 27th the average working rate 
of nitrification was reached. From this time to the end of the 
experiment the operation of this tank was practically constant,— 
occasionally influenced by changed conditions, as is shown in the 
tables of analyses, but quickly adjusting itself to these conditions. 

After the abandonment of No. 1 as a strainer, this tank 
was lowered to the level of No. 5, reconstructed as an aerator 
and known thereafter as 1 A. The construction was exactly 
like that of No. 5, save that the main body of the tank was 
filled with coke, crushed to the size of coarsely ground coffee. 
The outlet pipe was trapped by submersion in a tight wooden 
box of about 5 gallons capacity, which overflowed, through a 
wooden trough, into the large effluent tank. Samples of the 
effluent of 1 A for examination and analysis were taken from 
this box. The tank was first applied to this use August nth. 


18 THE PURIFICATION OF SEWAGE 

Nitrification appeared August 16th and rapidly increased until 
August 21 st. From this time to the end of the experiment the 
operation of this tank was practically constant. The results 
obtained in its use are fully set forth in the report of the 
chemical work. Its general performance was somewhat better 
than that of No. 5, and, on comparison, its effluent seemed to 
be whiter,— that is, more blue-white. 

In a strainer, during its period of use the voids of the 
material were completely filled by the flow of sewage. In an 
aerator, the voids were mainly filled by a constantly moving 
current of air, the liquid passing down, not in bulk, but in thin 
films, which worked their way over the surfaces of the particles 
of gravel or coke. The capacity of an aerator was, therefore, 
much less than that of a strainer of the same size. The effluent 
from the strainers was led to a distributing box, from which it 
escaped over a level weir, the flow being divided by movable 
knife-edge gates, which regulated the amounts applied to the 
aerators. Ordinarily No. 5 received one-fifth of the total flow 
from the strainers, and 1 A from one-fifth to three-tenths, the 
balance being returned to the sewer. At times two-fifths was 
turned into 1 A and satisfactorily purified. The amount of 
sewage actually passed through each tank daily, and the total 
flow in gallons per acre, are clearly shown in Tables A and E. 
The average daily flow through the strainers was at the rate of 
3,787,200 gallons per acre (the maximum was 8,950,194 gallons), 
and through the aerators at the rate of 1,064,213 gallons (the 
maximum, after nitrification began, being 4,826,112 gallons). 

The total flow applied to a strainer passed down through 
the central cylinder enclosed by the diaphragm, whose area was 
one-half that of the whole tank surface, and rose through * the 
ring outside of the diaphragm. In effect, the sewage passed 
through a cylinder of filtering material about 10 feet deep and 
with a section equal in area to the circle within the diaphragm. 
So far as the filtering capacity of the tank was concerned, it 
might have been constructed in this form, the speed of flow 
being regulated by an adjustable gate in the pipe at the bottom, 
from which, in this case, the effluent would have escaped. The 
rate of application, which is figured in the tables on the area 
of the whole tank—circle and ring, was, therefore, actually 


BY FORCED AERATION. 


19 


twice the amount stated, or an average of 7,574,400 and a maxi¬ 
mum of 17,900,388 gallons per acre. 

The average percentage of purification, as represented by 
the removal of organic nitrogenous matter, accomplished by 
the strainers alone, was 51.2, and by the strainers and aera¬ 
tors together 92.5. At one time a purification of 99.08 per 
cent, was reached. 

The sole function of the forced aeration was to supply 
oxygen to the interior of the tanks in sufficient quantity to 
excite and maintain the maximum activity of the bacteria of 
decomposition. It is probable-, however, that, although the 
constant presence of oxygen is necessary for constant purifica¬ 
tion, the amount actually consumed in the reduction of the 
organic matter is small and no additional benefit is derived 
from the supply of an excess. Towards the close of the experi¬ 
ment, the air-pipe of No. 5 was throttled by the insertion of a 
diaphragm, pierced, with f- and -f-inch holes, which could be 
closed at will with corks. These holes were plugged, one or 
two at a time, until the amount passing through one f-inch 
hole was the sole supply of the tank. Later this was closed 
and a f-inch hole opened, reducing the supply, theoretically, 
by three-fourths. No further change was made and the tank 
was operated with this amount of air until the close of the 
experiment. The effluent showed no signs of deterioration and the 
supply was probably ample. Whether or not any further reduction 
would be possible remains to be determined by future experi¬ 
ment. Probably a vigorous aerating of the filter for say five 
minutes in each hour, thoroughly changing the air in all its 
voids, would store sufficient oxygen to keep the bacteria active 
until the next period of aeration. This course would probably 
be wiser than an attempt to furnish a constant supply at a 
lower pressure, for, in the latter case, the air would escape in 
the lines of least resistance, and the more remote or compact 
portions of the filter would not be penetrated by it; while inter¬ 
mittent aeration at a higher pressure would force the air Into 
every crack and corner, and secure the efficient operation of 
all parts of the mass. By means of light partition walls or 
diaphragms the filtering material could be divided into sections, 
which could be aerated vigorously in turn. Assuming that the 
above suggestion of five minutes aeration in each hour should 


20 


THE PURIFICATION OF SEWAGE 


.prove practical, the entire filter could thus be satisfactorily 
operated with one-twelfth of the air and power which would 
be used if the aeration were constant. 

The station was dismantled and the tanks taken apart within 
the week following the close of the experiment (October 17th- 
24th). ^ The upper foot (approximately) of the central compart¬ 
ment of each of the straining tanks showed more or less accu¬ 
mulation of silt, probably the result of the few heavy rainfalls 
during which pumping was continued bringing much gutter 
mud to the tanks Below this, the material was apparently as 
clean as when first put in, the pebbles and white gravel looking 
as though they had just been taken from their native beach. 
In no part of the tanks was there any sign of organic matter 
or any suggestion of the hundreds of thousands of gallons of 
sewage which had been passed through them. The thin layers 
of sand on top of the aerators were black with sulphides, but 
all the material below this was sweet and clean. No impurities 
had been stored in any of the tanks. They had been detained 
and destroyed. All the conditions clearly indicated that the 
usefulness of the filters had become in no wise impaired, that 
they were capable of performing their functions indefinitely, and 
that, under proper management, no renewal of the filtering 
medium would be necessary. 

GENERAL SUMMARY. 

The operation of the experimental plant and the results 
accomplished are set forth in detail in the annexed report of 
the chemist in charge and the accompanying tables. Briefly 
summarized, these results demonstrate that:— 

1. The suspended matters of sewage (sludge) can be me¬ 
chanically withheld by straining slowly through suitable mate¬ 
rial. 

2. The filth accumulated by this straining material can be 
destroyed and the straining medium restored to a clean condition 
by mere aeration. 

3. The successive alternate operations of fouling and cleans¬ 
ing can be carried on indefinitely, without renewal of the strain¬ 
ing material. 

4. The purification obtained by this straining process prac¬ 
tically equals that accomplished by chemical precipitation, and 


BY FORCED AERATION. 


21 


is sufficient to admit of discharge into any considerable body of 
water not used as a source of domestic supply or for manu¬ 
facturing purposes requiring great purity. 

5. Practically, all of the dissolved organic matter in sewage 
can be removed and purification to a drinking water standard 
can be obtained by the use of suitably constructed bacterial 
filters. 

6. Such filters can be maintained in constant and efficient 
operation by suitable aeration. 

7. The erection of a plant capable of purifying large vol¬ 
umes of sewage upon a relatively small area calls for no costly 
construction. Repairs and renewals are merely nominal. The 
attendance required is but slight. There is no outlay for chemi¬ 
cals, etc. The only expense of mechanical operation is the 
driving of the blower or air-compressor. 

8. The process admits of wide variation in the selection 
of filtering material, and nearly every community can find, in 
its local resources-, something suitable for the purpose. 

The chemist in charge of the work, Mr. George W. Rolfe, 
was selected for the purpose by Prof. Thomas M. Drown, of 
the Massachusetts Institute of Technology and consulting chemist 
of the Lawrence experiments. He was specially fitted for it by 
a practical study of sewage purification at the Lawrence experi¬ 
ment station of the Massachusetts State Board of Health. He 
was assisted by Mr. Lorenzo Manuell. 

The plant was erected under the supervision of Mr. G. 
Everett Hill, who also directed its general operation. 


Acknowledgments are due to Prof. Thomas M. Drown, Prof. 
William T. Sedgwick, Mr. George W. Fuller and Mr. Allen 
Hazen for visits of inspection, for advice and for their cordial 
expressions of approval. 












































































' 

















































































■ 































REPORT 


OF CHEMICAL WORK AND GENERAL NOTES ON AN EXPERIMENTAL 
INVESTIGATION OF THE VALUE OF A PROCESS OF PURIFY¬ 
ING SEWAGE BY FORCED AERATION, 

INVENTED BY COL. GEO. E. WARING, JR. 

MAY 18 - OCTOBER 18, 1894. 


BY 

GEO. W. ROLFE, A. M. (Harv.) 


/ 
















•• 


















. 





* 

















































































































































































































Report of Chemical Work and General Notes. 


The figtires tabulated in this report express the results of 
an investigation covering five months, and having two specific 
objects: (i) To determine the efficiency of a new system of 
sewage purification; (2) To determine the duration of this effi¬ 
ciency. 

Means at our disposal limited the chemical work of this 
research to a study, made on the sewage and purified effluents, 
of the transformation of nitrogenous matters, an approximate 
estimate of carbonaceous matter by an indirect method of oxida¬ 
tion, the determination of dissolved oxygen and the determina¬ 
tion of chlorine. 

For aid in planning the chemical work I am indebted to 
Prof. T. M. Drown and his staff of able assistants of the Massa¬ 
chusetts State Board of Health laboratories, who have not only 
favored me with valuable advice on points of detail, but have 
furnished means of verifying the accuracy of our chemical 
standards by direct comparison with those in use in the Board 
of Health laboratories. I am also under obligations to Prof. 
Sedgwick, of the Biological Department, for advice. 

In the detail work of the experiment I have been assisted 
by Mr. Lorenzo Manuell. 

MEASUREMENT OF SEWAGE AND EFFLUENTS. 

The sewage applied was measured as follows. Determina¬ 
tions of the volume delivered at each pump stroke were made 
by averaging a sufficient number of actual measurements taken 
during the twenty-four hours. The number of strokes was re¬ 
corded by a revolution-counter, the occasional defective working 
of this being checked by a calculation based on regular observa¬ 
tions of the strokes per minute. Rates in gallons per acre were 



26 


THE PURIFICATION OF SEWAGE 


then calculated from these figures by factors expressing the 
actual proportional filtering areas of the tanks. 

As the aerators were proportioned for a relatively smaller 
flow than the strainers, a fraction of the effluents of the latter, 
measured by a special adjustable apparatus, was applied, the 
rest being thrown away. 

CORRECTION FOR DRAININGS. 

The construction of the straining tanks required them to 
be drained through the bottom just before aeration. In this 
experiment it was not thought important to recover the drain¬ 
ings, hence corrections for this loss have been made in rates of 
tanks affected thereby. 


CONTROL OF FLOW OF SEWAGE AND EFFLUENTS. 

The amount of sewage applied could be controlled only to 
a limited extent by (i) altering the discharge of the pump by 
a crank adjustment, (2) varying the speed of the machinery by 
increasing or decreasing the electrical resistance. The flow of 
strainer effluents passing into the aerators could be absolutely 
controlled by adjustment of the distributing apparatus. 


CIRCUMSTANCES AFFECTING FLOW OF SEWAGE 
AND EFFLUENTS. 

The flow of both sewage and effluents was, however, subject 
to wide daily variations, due to (1) changes in electromotive 
force, (2) occasional stoppages from breakdowns of machinery, 
(3) rains, (4) very high tides. These circumstances, in great 
part, could neither be foreseen nor provided for, and necessi¬ 
tated much complication of records. 

The more important data of pumping and blowing will be 
found conveniently arranged in Table A. This table is valuable 
for interpreting all rate figures, as calculations are made from 
the sewage actually pumped in twenty-four hours, regardless of 
stoppages. 


BY FORCED AERATION. 27 

NOTES ON SEWAGE AND THE CONDITIONS AFFECT¬ 
ING ITS QUALITY. 

The sewage of Newport, besides being largely influenced 
by storm-water, is affected by the following peculiar conditions. 
(1) Variations in .flow caused by fluctuation of back pressure at 
outlet, due to tides. (2) Occasional invasions of salt water caused 
by very high tides (over four feet rise) which back salt water up 
the main sewer for a long distance. (3) Dilution and disturb¬ 
ance caused by extensive washing of streets and catch-basins 
with city water at frequent and irregular intervals. (4) Partial 
putridity, due to overflows from cesspools and deposits in the 
sewers. 

The effects of rain and salt water have been, in most cases, 
eliminated by stopping the pump at times when the state of the 
weather or tidal calculations indicated the probability of abnormal 
conditions. The periodic reversal of flow, caused by the tides, 
fills the large sewers along the level shore streets for long dis¬ 
tances, and mixes the sewage, so that it is doubtful whether 
there is any regular variation in strength from hour to hour at 
the sewer outlet. The prevalent use of cesspools of course con¬ 
tributes to the same result. Samples taken at different hours 
in the day showed no marked differences when analyzed. In 
one instance (August 27) a representative sample was taken at 
intervals covering the twenty-four hours, except between 1 and 
5 a. m. This sample practically agreed with the regular samples 
of the week taken about 9 a. m. 

There are good grounds, therefore, for assuming that the 
analyses, in the main, represent the quality of the sewage enter¬ 
ing the tanks. Probably this was somewhat stronger than the 
average flow, as the suction pipe was but a few inches above 
the bottom of the sewer, the stream being sluggish at all times 
except at low tide. 

Disturbances due to flushing catch-basins, which occurred 
almost daily in some part of the city during dry weather, and 
were occasionally evidenced in the sewage, could not be provided 
against, nor could their influence be calculated. Probably they 
did not affect the result seriously. 

In the latter part of June, signs of gas-liquor appeared, but 
its presence was not proven. Noticeable quantities of dissolved 


28 


THE PURIFICATION OF SEWAGE 


oxygen were found in the sewage of June and July. This dis¬ 
appeared August ioth, not to reappear until October 6th. The 
general characteristic appearance of the sewage was quite uni¬ 
form, being greyish and milky. This was principally varied by 
silt and fibrous matter, which rapidly subsided on standing. As 
a rule, the odor was faint in samples just taken, often that of 
stale urine, although at times, noticeably on Mondays, there was 
a distinctly soapy smell. 


SAMPLING. 

Many circumstances prevented the control of conditions nec¬ 
essary for a uniform system of sampling. In every case the 
aim has been to await opportunities most favorable for getting 
data fairly representing the working of the system in actual 
practice, rather than to accumulate many figures obtained un¬ 
der doubtful conditions. 

All samples of sewage for general analysis were taken from 
the discharge pipe of the pump while pumping. 

As the purpose of the apron was simply to remove coarser 
stuff, such as paper, leaves, cloth and clotted matter of a gela¬ 
tinous and greasy nature, which tended to form an impervious 
scum on the surface of the tanks, and as the amount of matter 
retained was very variable, since the stones were often dis¬ 
turbed by raking, no analyses of the apron effluent were made. 
Its work was reckoned in with that of the tank into which it 
delivered. 

Samples of strainer effluents, except when otherwise speci¬ 
fied, were taken from the faucet H, about six inches below the 
overflow pipe. 

Sampling of the aerator effluents was done at the traps of 
their discharge pipes. 

Attempts were made to trace sewage of the definite compo¬ 
sition represented by the sample from tank to tank by deter¬ 
mination of the chlorine in the effluents. This was usually un¬ 
successful, because of diffusion in the three or four hundred 
gallons held in the tank, and the rapid fluctuation of chlorine 
salts due to small quantities of salt water getting into the sewer 
in spite of precautions. In one case, where the experiment was 
carefully conducted with special reference to the point of tra- 


BY FORCED AERATION. 


29 


cing the sewage, great discrepancies were found in the chlorine, 
only to be accounted for by diffusion. 

The straining tanks were drained very gradually from the 
small faucet F, to avoid dislodging matter deposited upon the 
stones. Analyses show that the loss was so small as to be neg¬ 
ligible (e. g. No. 4 regular sample effluent: albuminoid ammo¬ 
nia = .025; drainings = .037). 

METHODS OF ANALYSIS. 

In general, the practice of the Massachusetts State Board of 
Health was followed. 

As a rule, all samples were analyzed immediately after col¬ 
lection. 

The distilling apparatus was, in its main features, patterned 
after the one in use at the Lawrence experiment station, but 
necessarily modified for kerosene stoves. About .01 gram of 
ammonia-free sodic carbonate was added to the sample to be 
distilled. 

Nitrites were determined by the naphthylamine method of 
Griess; nitrates by the phenoldisulphonic process. Samples were 
evaporated at a very gentle heat on asbestos paper placed over 
incandescent lamps glowing at a dull red. Owing to the pres¬ 
ence of chlorine, these nitrate figures are perhaps too low, but 
are useful as comparative tests. 

“Oxygen consumed,” useful as a comparative estimate of car¬ 
bonaceous matter, was made by the Kiibel “hot acid” method. 
Dissolved oxygen was determined by Winkler's method, correc¬ 
tions being made for nitrites present; chlorine by process rec¬ 
ommended by Hazen. 

OTHER LABORATORY DATA. 

Temperature records were kept, covering most of the samp¬ 
ling. 

Measurements of rainfall were made by weighing the precip¬ 
itation in grams and tenths on an area of 100 square centi¬ 
meters. This was done by means of a copper rain-gauge of 
approved construction, which was placed on the laboratory roof. 
The results are given in millimeters. 


30 


THE PURIFICATION OF SEWAGE 


“PER CENT. OF PURIFICATION” FIGURES OF EF¬ 
FLUENTS. 

The offensive nature of distillates, showing large amounts of 
free ammonia, has led to the belief that this test really repre¬ 
sents not only ammonia and its salts, but also many unstable 
organic compounds possibly of the nature of amines, which, 
though they may evolve ammonia when heated, are really in¬ 
termediate products of putrefaction. 

It was decided, therefore, to estimate purification by meas¬ 
uring the removal of all nitrogen obtained in the form of am¬ 
monia. In the absence of any established factor for calculating 
absolute total albuminoid ammonia from “albuminoid ammo¬ 
nia” as obtained by the Wancklyn method, the following for¬ 
mula for reckoning total nitrogen as ammonia was adopted:— 

Total nitrogen as ammonia = “Free Ammonia” -f- 2 (“Al¬ 
buminoid Ammonia”). This holds good for most surface 
waters and is approximately correct for sewage;* at least, it 
furnishes a fairer basis of comparison, it is believed, than the 
“albuminoid ammonia” figures alone. 

“Per cent Purification,” therefore, in columns marked 
“Total,” is the direct ratio of the total nitrogen of the effluent 
of the tank named to the total nitrogen of the sewage, and rep¬ 
resents the total purification of the sewage as shown by that ef¬ 
fluent. “Percent. Purification,” in columns marked with num¬ 
ber of tank, is the ratio of the total nitrogen of the effluents 
specified to the total nitrogen of the affluent of that tank, and 
indicates the amount of purification accomplished by the tank 
independently. 

METHODS OF INVESTIGATION OF MATTER RE¬ 
TAINED BY FILTERS. 

Owing to lack of facilities, as previously stated, but little work 
was done in investigating the amounts of organic matter 
retained by the strainers and destroyed by aeration. 


*Recent study of a number of Kjeldahl determinations and “albumi¬ 
noid ammonias” made on artificial sewages places this factor at about 
2.4. 



BY FORCED AERATION. 


3i 


Great difficulty was met in sampling the filtering material 
properly. Apparatus fitted to each tank for this special purpose 
proved inefficient. Sampling, which was, therefore, done with 
an ordinary shovel, was limited to shallow depths. For the 
rough comparative tests which could be made, the filtering ma¬ 
terial was dug into carefully to a depth of one foot. About 
one litre of the gravel at that depth was transferred to a large 
saucepan with an equal volume of distilled water, and vigor¬ 
ously stirred with a glass stirring rod for exactly five minutes. 
At the end of that time all matter visible to the eye was re¬ 
moved from the stones by the washing. The turbid liquid was 
quickly poured off, before it had time to settle, and, with the 
same precautions, was diluted to ^ or t ^~q, according to cir¬ 
cumstances. Ammonia determinations of this were then made 
in the manner of testing sewage. 

The few results obtained are arranged in Table D. The 
only complete series of tests for a single period of aeration was 
made of the gravel of No. 4. This was done at the one time 
when circumstances were especially favorable for the work. 

MICROSCOPICAL AND BACTERIOLOGICAL WORK. 

No bacteriological cultures were attempted because of lack 
of facilities. The very few desultory microscopical examina¬ 
tions which were made of sewage and effluent of strainer No. 
4 are hardly worthy of record. A very characteristic bacterium 
noticed in the sewage, plump, very motile and usually doubled, 
corresponded closely to the description of B. cloacae , of the Law¬ 
rence reports. On the surfaces of the stones in the top of the 
outer compartment of No. 4, in August, amoebae were noticed 
feeding on numerous algae, among which were recognized 
scenedesmus and protococcus. There were also present multitudes 
of large speckled spirilla, exceedingly motile. About 20 per 
cent, of dissolved oxygen was present in these upper layers, 
although none was found in the body of the tank. 

NOTES EXPLANATORY OF TABLES C AND E. 

In Table E are given all data necessary for understanding 
the work done by each tank and the resulting purification, fig¬ 
ured from analyses of sewages and effluents as previously ex¬ 
plained. 


32 


THE PURIFICATION OF SEWAGE 


The first two sets of pumping and aerating periods, extend¬ 
ing from May 17th to June 2d, were not arranged with special 
reference to state of effluents or condition of tanks, but were 
merely trial trips, as it were, made to gain familiarity with the 
working details. No systematic chemical tests were made at 
this time, the laboratory arrangements being incomplete. Rate 
figures were taken, but their accuracy is somewhat impaired by 
the numerous leakages caused by the dry woodwork of the new 
spouts and tanks. 

On May 18th, a heavy thunder-storm, precipitating 21.9 
mm. of rain in two hours, washed considerable silt into the 
tanks, especially into No. 1. A repetition of this was guarded 
against, as Table A shows. Table A will also sufficiently ex¬ 
plain most of the irregularities in times of testing samples. 

July was practically lost to our investigation on account of 
numerous difficulties with the pumping machinery. At such 
times the laboratory became an improvised machine shop. Re¬ 
pairs of apparatus also compelled the omission of chemical work 
for ten days at the end of August. 

The regular chemical work closed October 13th. Pumping 
continued till October 18th, when the tanks were taken apart 
and the experiment station dismantled. 

WORK DONE BY APRON. 

The two compartments of the apron were used alternately, 
each working as long as it could pass sewage. This time de¬ 
pended largely on the amount of silt in the sewage and on con¬ 
ditions discussed in the next section. Notes giving data of the 
working of the apron will be found in Table B. 

The stones were frequently raked and when badly clogged 
were washed, the washings going into the harbor. In a large 
plant, where the arrangements were better, raking alone would 
no doubt suffice for removing the coarser and more fibrous 
matters. The finer impurities in the mass would be destroyed 
by natural aeration during a period of rest. 

The efficiency of the apron was greatly increased by the 
use of a screen of coarse wire netting, which was added in the 
early fall. 

Considerable swill was among the matter caught by the 
apron. 


BY FORCED AERATION. 


33 


NOTES ON WORK OF STRAINERS. 

At first the sewage was passed through the whole series of 
tanks. The analyses soon made it clear that the bulk of the 
work was done by the first strainer. Indeed, not infrequently 
an increase in nitrogenous matter was shown in the effluent after 
leaving the first tank, especially when the rate of flow was 
slow. This seemed to be due to putrefaction of stored nitro¬ 
genous matter, resulting in the production of soluble com¬ 
pounds. It naturally manifested itself as “free ammonia.” 

The use of two straining tanks, in series, proved more sat¬ 
isfactory, but the filtering surface of the second tank was out 
of all proportion to the purification obtained. From August 
13th to the end of the experiment but one strainer v/as used at 
a time, the others meanwhile aerating. 

PERIODIC USE OF STRAINERS. (See Table E.) 

It was intended to establish definite periods for passing 
sewage and for aerating, but it was found impracticable, in part 
from causes affecting the regularity of the work. ( Table A.) 

As a rule, sewage was passed through a strainer until the 
resistance was so great that the gradual accumulation in the in¬ 
ner compartment overflowed the diaphragm. This resistance re¬ 
sulted from the collection of matter of a gelatinous or greasy 
nature in the interstices of the stones, and also from a practi¬ 
cally impervious drab scum, which formed on the surface to a 
depth of about half an inch. The rate at which this clogging 
matter gathered was very variable and depended upon obscure 
conditions of the sewage. It was noticed that an admixture of 
salt water materially increased it, evidently from precipitation 
of soap; and that putrefaction, as has been indicated, tended to 
decrease it by making soluble compounds. 

The running period of a tank could be increased, perhaps 
a day, by frequent raking of the scum on top of the stones. 
Once or twice, as shown in the notes of Table R, the sewage 
was drained down below the stones and the scum scraped off. 
This did not extend the period of operation materially. Deep 
raking (about 6 inches) and a stirring up of the stones with an 
iron bar to a depth of more than 3 feet, as was tried a week 
or more with No. 2, proved of no marked benefit. The latter 


34 


THE PURIFICATION OF SEWAGE 


feature would be impracticable on a large scale. A deep rak¬ 
ing, it is true, immediately lessened the resistance, but the re¬ 
lief was only temporary. 

This fact makes it evident that the clogging was caused 
principally by material retained in the upper layers, and sug¬ 
gests that oxidation, if not the escape of carbon-dioxide, may 
be influential in forming the scum. This supposition is strength¬ 
ened by the fact that it forms equally on tanks receiving 
strained effluent and also that effluents drawn from the interior 
of a tank increase their cloudiness perceptibly while standing a 
short time. Unfortunately, no tests for dissolved oxygen were 
made in these upper layers, except in one case, where its pres¬ 
ence could be explained by algae. Three inches belcnv the upper 
surface of the stones no dissolved oxygen was present, as was 
proved by many tests. 

STRAINING-TANK EFFLUENTS. 

The effluents of all the strainers had the same characteris¬ 
tics. In appearance they were greyish and translucent, resemb¬ 
ling water to which a very small quantity of milk had been 
added. This cloudiness varied considerably in different speci¬ 
mens, and in the same sewage, when passed through successive 
tanks, showed a gradual decrease. Salt water, as would be ex¬ 
pected, increased it. Effluents which had passed slowly through 
a series of tanks often showed a darkening from putrefaction. 

All strainer effluents darkened and began to putrefy in 
about twenty-four hours. When taken from the bottom of a 
strainer they were always partly putrid, and contained slightly 
more albuminoid as well as free ammonia. These effluents' de¬ 
posited no sediment after long standing. The odor was usually 
marked, and of stale urine. Dissolved oxygen was invariably 
absent, except in one case cited in the next section. 

No relation could be traced between the condition of the 
filtering material or size of stones and the quality of the efflu¬ 
ents, except in one case, where, after a long aeration, there 
were evidences of oxidation products washed out of the stones. 

MEASUREMENTS OF TURBIDITY. 

From time to time rough determinations of the turbidity 
of sewage and effluents were made by an apparatus contrived 


BY FORCED AERATION. 


35 


to measure the maximum depth of liquid through which the 
markings of a millimeter scale, printed in black on a white 
ground, could be read, when illumined by a good light (day¬ 
light). 


Two examples, 

— strainers 

running in 

series, —will 

ciently illustrate the method : — 

No. 1. 

No. 2. 

Sewage, 


30 mm. 

45 mm. 

Effluent from Apron, 

42 “ 

42 “ 

u u 

No. 1, 

81 “ 

144 “ 

u << 

No. 2, 

165 “ 

213 “ 

<( a 

No. 3, 

33 i “ 

390 “ 

a a 

. No. 4, 

400+ 

600-f- 


AERATION OF STRAINERS. 

Before aerating, the black scum which practically sealed 
the top of the filter was either broken up or scraped aside. 
The foul odor given off at the beginning of aeration, which was 
hardly noticeable except to one standing directly over the tank, 
disappeared in three or four hours. In this odor there was often 
recognized a faint smell resembling the “sludge-acid” of the 
oil refineries, and it is probable that it was caused by traces of 
light petroleum oil, presumably kerosene. 

After about a day’s aeration, the scum dried up into thin 
clay-like cakes, and the stones, which were at first covered with 
a black slime, began to take on the ordinary greyish-white ap¬ 
pearance of dusty gravel, the black color probably being due 
to ferrous sulphide. 

Immediately below the surface, where the stones remained 
moist, and in spots where the clotted matter opposed the passage 
of air, there would be, at times, a vigorous growth of white 
mould. This mould, however, never extended downward more 
than three inches, and soon disappeared as the aeration pro¬ 
gressed. Below this the stones were thinly coated with a trans¬ 
parent jelly-like slime, practically odorless, or, at most, having 
a faint fishy smell. This feature remained, with no perceptible 
change, during the entire period of aeration. 

The air-pressure varied from 2 to 4 inches, water-column, 
in the main air-pipe. The air current coming out of the stones 


36 


THE PURIFICATION OF SEWAGE 


was usually barely perceptible to the moistened palm held just 
above the stones. 


LENGTH OF AERATION. 

In general, the time of aeration of any strainer depended 
solely on the running period of the others, each tank aerating 
till its turn to run came in regular rotation. 

In one instance, the aeration of No. 2 was prolonged for a 
month. In another, No. 3, after passing over 15,000 gallons 
(nearly 30,000,000 to the acre), had only four days aeration, 
and then took 41,000 gallons (81,000,000 to the acre) before 
clogging. In neither of these cases did the effluents, as a whole, 
show any sign of the great difference in length of aeration pe¬ 
riods. The effluent of No. 2, however, when the tank was just 
starting again , was unique in having (1 ) an enormous quantity 
of nitrites, (2) a large amount of dissolved oxygen and (3) a 
slight amount of nitrates, all of which, of course, came from 
the material in the tank. 

Careful study of the results clearly showed that the time 
necessary for aeration depends largely on the thoroughness of 
the exposure of the upper layers of the filtering material to the 
action of the air. If the scum is removed or piled loosely in 
heaps after partial drying, and the matter between the stones 
thoroughly disintegrated to a depth of about six inches, by rak¬ 
ing or plowing on the second day, the time of aeration is re¬ 
duced to three or four days, while double this time does not 
suffice without such treatment. Further experiments are neces¬ 
sary to establish the minimum period of aeration for practical 
work. 

AERATORS. 

No. 5 aerator received sewage throughout the whole exper¬ 
iment, except (1) during removal of scum from the surface of 
the sand, (2) a few hours on June 22nd, when the shallow lay¬ 
er of fine sand on top was replaced by coarser sand, and (3) 
September 5th to 7th, during repairs to the upper air-space of 
broken stone. 

No. 1 A was constructed during the early part of August 
by removing the coarse stone and wooden diaphragm from No. 
1 strainer, and converting it into an aerator on exactly the same 


BY FORCED AERATION. 


37 


plan as No. 5. Coarsely powdered coke was used as the main 
filling 1 , instead of fine beach gravel. No. 1 A was started 
August 8th, and continued in use for the rest of the experiment, 
except when stopped for removal of scum. 

In the early part of September, very little air passed out 
of the flues of No. 5, showing, apparently, that the air-space 
was clogged. September 5th, the flow was stopped and an in¬ 
vestigation made. The broken stone of the air-space and the 
gravel beneath were found to be absolutely clean, and the trouble 
was traced to the unequal sizes of the stones, which had become 
packed together in the air-space. This was remedied, and the 
tank gave no more trouble for the rest of the experiment. 

EFFLUENT OF NO. 5. 

The effluent of No. 5 was somewhat milky at first. This 
continued, to a slight extent, even after nitrification was estab¬ 
lished, but gradually disappeared. About the middle of July it 
was as clear as ordinary pond water, and had the characteristic 
color of the public water supply (.7 to .8 Nessler). 

At times, after any considerable disturbance of the sand by 
deep raking (2 to 3 inches), as practiced in July and early 
August, the effluent showed milkiness for a few hours. This 
was attributed to the opening of channels through the sand, 
through which the liquid passed rapidly in streams, descending 
through small areas of gravel instead of being distributed over 
the stones in thin films. 

An extensive growth of cretiothrix , which suddenly appeared 
in the effluent on June 24th, and which disappeared in twenty- 
four hours, never to return, is attributed to this same cause, — 
the passage of a large amount of liquid through a small portion 
of the tank, with consequent imperfect aeration. 

The use of a rake, specially constructed so that the scratch 
ings could not exceed half an inch in depth, removed this 
trouble, the only recurrence of cloudiness in the effluent follow¬ 
ing the starting of the tank September 7th, after repairs. This 
was obviously due to defective distribution, for when the soak- 
age of the sand was sufficiently increased by partial clogging, 
the cloudiness quickly disappeared. 

Often, in August, large quantities of white thread-like worms, 
about a quarter of an inch long, and particles of water plants 


38 


THE PURIFICATION OF SEWAGE 


were carried out of the tank by the effluent. These quickly 
settled to the bottom of the trap, and did not seem to affect 
the quality of the water. Being obviously growths of the air¬ 
spaces, they were not reckoned as part of the effluent. 

From the beginning, the effluent was odorless, or rarely 
had a faint loamy smell, such as may be noticed in a green¬ 
house. 


EFFLUENT OF NO. i A. 

The effluent of No. i A, which showed nitrification within 
four days, was in general, better than that of No. 5, and was 
practically free from suspended organic matter, save for infre¬ 
quent white flocculent masses of zoogloea. No worms were ever 
noticed. The fact that the trap was covered accounts for the 
absence of higher water plants. Deep raking of the sand on 
top produced, as in No. 5, cloudy effluents. The trouble dis¬ 
appeared after using the special rake before described.* 

In other characteristics the effluent resembled that of No. 
5, but at first was somewhat lighter colored from the decolor¬ 
izing action of the coke. 

On August 19th two large minnows were placed in the 350 
gallon tank, which received the effluents from Nos. 5 and 1 A. 
These fish apparently thrived till September 2nd, when one died, 
the other surviving till September 4th. It is possible that they 
died of starvation. 

EFFICIENCY AND DAILY CAPACITY OF AERATORS. 

Assuming normal sewage and nitrification established, the 
satisfactory operation of an aerator, similar in principle to those 
used in this experiment, apparently depends on (1 ) the efficiency 
of the means for distributing the sewage in thin films to the 


* The following analyses illustrate the variable effects of disturbance of 
sand on aerator effluents : — 

Free Ammonia. Alb. Ammonia. 
No. 5, just after raking, .025 .094 

No. 5, about two hours later, .012 .082 

No. 1 A, just after raking, .070 .250 

No. 1 A, about two hours later, .006 .040 

The high ammonias of No: 5 on August 25th and September 21st can 
also be traced to the same cause. 



BY FORCED AERAT/OJV. 


39 


action of the nitrifying organisms, (2) an air supply sufficient 
to maintain the activity of these organisms, (3) a flow slow 
enough to ensure a sufficiently long exposure of the sewage to 
the purifying organisms within the filter, and (4) favorable 
temperature. 

In the case of Newport sewage, the only really abnormal 
conditions were caused by the occasional influx of salt-water, 
in quantity sufficient to check nitrification. This occurred in¬ 
frequently. 

The air supply was always in great excess, as was shown 
by the following experiment with No. 5. About October 1st, 
the amount of air going through this tank was reduced by plac¬ 
ing in the 8-inch air-pipe an air-tight wooden diaphragm, per¬ 
forated with holes of different sizes. These holes were closed 
a few at a time, until, on October 6th, the opening was re¬ 
duced to a diameter of f inch. On October 8th, this was 
diminished to -§ inch. The tank continued giving an effluent of 
undiminished purity for the rest of the time it was in use. It 
is to be regretted that lack of time prevented further experi¬ 
ments in this direction. 

Temperature conditions were beyond our control, but there 
is no reason, in the light of present ■ knowledge, for believing 
that they were not most favorable during the whole period that 
the work was going on. It must not be overlooked that the 
problem of working an aerator on this plan, when exposed to 
a severe northern winter, has not yet been solved experimentally. 
The chilling effect of the outside air forced through the tank 
would be a serious consideration.* In the majority of cases, 
however, this difficulty could probably be obviated by suitable 
arrangements for drawing the air supply from the sewers them¬ 
selves. 

In the experiment at Newport, the air supply and temper¬ 
ature being constantly favorable for the highest efficiency, and 
sewage practically normal, there remain to be considered the 
questions of distribution throughout the filter and rate of flow. 


*It is interesting to note that in some later experiments (January, 1895), 
I have found good nitrification in an effluent leaving the tank at a tem¬ 
perature of 35 0 F., and probably at no time in its passage having a tem¬ 
perature greater than 45 0 . 



40 


THE PURIFICATION OF SEWAGE 


The means at first employed for distributing the strainer effluent 
throughout the aerator was a 6-inch layer of sand, of such fine¬ 
ness that the liquid passing through it soon wetted the whole 
area. For a time this worked very well, but the sand soon be¬ 
came covered with a scum and much clogged by material of 
the same nature as that which choked the gravel of the strain¬ 
ers, but in much less quantity. Raking the sand about 2 inches 
deep produced irregular distribution by the channeling mentioned 
in the discussion of aerator effluents. Use of the special rake, 
before referred to, stopped this, but it was then found that the 
sand would not pass sufficient strainer effluent for the capacity 
of the tank. A coarser sand was then substituted, which did 
not distribute satisfactorily at first, the liquid sinking into it 
within a few inches of the point at which it was delivered. 
The most satisfactory remedy proved to be fine sand sprinkled 
over the surface of this coarse sand. 

The best method found for preserving the constant and 
maximum operation of the aerator was — to stop the tank when 
it showed signs of clogging and scrape off the dirty sand on 
top, repeating this at successive cloggings till the thickness of 
the sand was so reduced that a fairly constant equilibrium would 
be established between the amount of sewage the sand would 
pass and the quantity the tank could purify in a given time, as 
shown by quality of the effluent. This established the rate for 
the maximum efficiency. The further treatment necessary was 
periodic removal of scum, shallow scratchings with the special 
rake, and occasional renewal of a worn place with a little sand. 

Only two kinds of sand were used. These were both fine, 
with not very uniform grains. As stated above, the coarser 
worked well, although it is my opinion that a still coarser sand 
would have been more satisfactory. Probably any fairly coarse 
sand, within quite wide limits of variation in size and uniform¬ 
ity of grain, will make a satisfactory distributor, provided that 
in the beginning a temporary layer of fine sand is used. In a 
short time this can be removed, as the clogging will impart 
sufficient capillarity to ensure even soakage. The next step is 
to determine the thickness of the layer which will allow suffi¬ 
cient strainer effluent to pass for the maximum capacity of the 
aerator, when producing the required degree of purification. 
Apparently this depends more on the nature of the sewage-than 


4i 


BY FORCED AERAT/OJV. 

on the size of sand. Speaking generally, coarse sand will give 
the best satisfaction and will require the minimum amount of 
attention if worked on the lines indicated. 

It is also advisable to divide the surface of the aerators in¬ 
to sections of comparatively small area, by partitions extending 
a few inches below it, so that a section can be raked or scraped 
without interfering with the work of the rest of the aerator. 
With an aerator working continuously at its maximum capacity, 
purifying sewage similar to that of Newport, scraping would 
have to be done at least every other day. 

The rate of maximum efficiency of No. 5, assuming a re¬ 
quired purification of 96 to 98 per cent., I place between 800,- 
000 and 1,000,000 gallons per acre. That of No. 1 A between 
1,200,000 and 1,500,000 gallons. The actual daily average of 
sewage applied was considerably less, owing to irregularities in 
pumping and frequent stoppages for experimenting with raking, 
removal of scum, etc. The working rates of the aerators were 
also largely reduced at times of changing straining tanks, as the 
drainings were lost and the flow to the aerators ceased until 
the new strainer was filled to the overflow point, say for three 
or four hours. In actual practice, these drainings should be de¬ 
livered to the aerators while the strainer just started is filling 
up. 

The figures given in the tables show the actual performance 
of the tanks under the unsettled conditions of experimental 
work. Hence, as a whole, they obviously cannot be taken as 
representing the full capacity of a plant constructed in the light 
of knowledge acquired and regularly operated under conditions 
of actual practice. 

I attribute the greater efficiency of the coke tank to the 
greater distributing surface of its irregular masses and their 
porous nature. The gravel masses, being approximately spher¬ 
ical, would have for their size a minimum amount of surface. 

A DETERMINATION OF TIME OF PASSAGE OF LIQ¬ 
UID THROUGH AN AERATOR. 

June 19th an attempt was made to determine the time of 
exposure of the liquid to the action of the aerator, under the 
conditions then existing. 


42 


THE PURIFICATION OF SEWAGE 


On the afternoon of that day No. 5 was receiving strainer 
effluent at the rate of .43 gallons per minute,—equivalent to 
1,195,000 gallons per acre per day,—and giving a purification, 
as shown by test the next morning, when conditions were prac¬ 
tically the same, of 71.0 per cent., carrying the total purifica¬ 
tion to 80.1 per cent. Nitrification was not fully established at 
this time. 

At 3.08 p. m., 1.54 gallons of salt water were thoroughly 
stirred into the affluent standing on top of the tank, estimated 
at nearly 56 gallons, and having a chlorine content of 7.60 parts 
per 100,000. The salt water raised the chlorine in the mixture 
to 55.0 parts, as shown by test. The chlorine in the effluent leav- 


ing the aerator 

at trap 

was 





at 3.14 p. m. 

7.70 parts 

at 4.08 

p. m. 

27.50 parts 

3-24 

7-35 

«< 

4.11 


23-50 

4 4 

3-29 

10.20 

<< 

4.14 


23 - 5 ° 

4 4 

3 - 3 i 

12.30 

<< 

4.17 


25-5° 

4 4 

3-34 

16.00 

4 < 

4.23 


26.00 

4 4 

3-36 

17.00 

< < 

4.27 


25.00 

4 4 

3 - 3 S 

18.50 

< < 

4 - 3 1 


25-25 

4 4 

3 - 4 ° 

I 9 - 5 ° 

1 < 

4-34 


25.00 

44 

3 - 42 i 

21.00 

11 

4-39 


25.00 

4 4 

3-45 

21.50 

11 

4 . 4 i 


25.00 

44 

3.484 

22.00 

(< 

4.44 


24.5° 

4 4 

3.52 

22.50 

< 4 

4-53 


24.5° 

4 4 

3-55 

23.25 

44 

5.06 


24.50 

4 4 

3-59 

24.00 

44 

5-33 


24.40 

4 4 

4.02 

24.50 

4 4 

5-47 


16.75 

4 4 

4.05 

26.00 

4 4 





The only determinations of 

chlorine 

made 

on the 

mixture 


on top of aerator were 


at 3.08 7.60 parts 

after mixture 55.00 “ 

4 - 5 ° P- m. 17.50 “ 

A study of the figures shows that within twenty minutes 
salt water appeared in the effluent, the amount assuming a 
practically constant proportion at the end of fifty minutes, 
reaching a maximum (42 per cent.) ten minutes later, but show- 
ing, during the whole subsequent period of over seventy min¬ 
utes that the experiment was followed, less than 7.5 per cent. 



BY FORCED AERATION. 


43 


variation. Putting the results in another way : —After about 21 
gallons of the mixture, approximately equivalent to 7.5 per cent, 
of the voids in the wetted gravel, had entered the tank, the 
diffusion was practically uniform throughout the entire effluent, 
which if then sampled would best represent the original af¬ 
fluent. 

This experiment, of course, only illustrates the work of the 
tank under one fixed set of conditions. By itself, it is valuable 
as evidence that the distribution in No. 5 was very good, and 
that like results might be expected in aerators of similar con¬ 
struction. It also proves that, when the rate was about 1,000,- 
000 gallons per acre, the effluent of No. 5 passed through the 
tank within an hour, with good purification. It further indi¬ 
cates that the amount of liquid distributed through the tank over 
the surfaces of the filtering material was between 20 and 25 gal¬ 
lons, or about 45,000 gallons per acre. 

SUMMARY. 

Careful study of the accumulated evidence leads to the fol¬ 
lowing conclusions: — 

(1). A straining tank, constructed on the plan herein de¬ 
scribed, can be depended upon to remove at least forty per cent, 
of the nitrogenous matter in ordinary sewage, if this sewage, 
rough strained and free from mud, is applied continuously at 
the minimum rate of three million gallons per acre in twenty- 
four hours. 

(2 ). The gross amount of sewage which such a strainer 
will take before clogging depends principally on variable con¬ 
stituents of the sewage, but also, to some extent, on the size of 
the voids of the filtering medium. For ordinary materials, with 
voids of not less than 30 per cent., and with particles larger 
than .20 inch, the minimum can be placed at 20,000,000 gallons 
per acre pnoaiwhen the sewage is applied continuously. 

(3 ). If the thick sludge is removed and the upper 6 inches 
of the filtering bed opened up by raking or plowing after the 
filter is drained, an aeration period not exceeding five days is 
sufficient to quite restore the strainer to its original efficiency. 

(4). Further experiments are necessary to determine the 
smallest efficient air-supply for the cleaning of the strainers. It 
is much less than that used in the investigation. 


44 


THE PURIFICATION OF SEWAGE 


(5 ). The efficiency of a strainer is little affected by the in¬ 
creasing amount of matter retained, up to the time of clogging ; 
nor, within wide limits, is it influenced by the size or shape of 
the particles of the filtering medium. 

(6). The strainer will preserve its efficiency indefinitely. 

(7 ). An aerator, constructed on the plan herein described, 
after nitrification is established, and the methods of distribution 
properly adjusted, will remove over ninety-five per cent, of the 
organic nitrogen of a strainer effluent, applied at a rate of at 
least 800,000 gallons per acre per day. It will continue to do 
this for an indefinite period, providing suitable arrangements are 
made for removing sludge at frequent intervals. 

(8). A reduction of at least 75 per cent, can be made in 
the air-supply to the aerators, as used in this investigation, with¬ 
out impairing their efficiency. 

( 9). Of coke and gravel, of practically the same size, used 
in aerators of similar design, the coke purified over 20 per cent, 
more sewage than the gravel. 


ANALYTICAL TABLES. 


TABLE A.— RECORD OF PUMPING AND AERATING. 


46 RECORD OF PUMPING AND AERATING. 


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RECORD OF PUMPING AND AERATING . 


47 






















































TABLE A.— RECORD OF PUMPING AND AERATING ( continued ) 


48 


RECORD OF PUMPING AND AERATING. 


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TABLE B. — ANALYTICAL DATA OF SEWAGE AND EFFLUENTS. 


5 ° 


ANALYTICAL DATA OF SEWAGE. 


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TANK No. 3. TABLE B. ( continued ). 


54 


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TANK No. 5. TABLE B ( continued ). 



TANK NO. 5. 


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TANK No. i a. TABLE B ( continued ). 


58 


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TABLE B ( concluded ). 


CITY WATER FROM LABORATORY. 


59 


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Analyses arranged by days. TABLE 


60 


TABLE C. 


V 


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TABLE C. 


61 





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o o o o 


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OOCOON CO O CO Cl Cl 00 CO vo O CNONN Cl ON CN O CO Tf- ON Tf- 1 -H Tf vO CO Tf- m Tf Cl 

oo ci o ci ci — h h tj-h h cj n h o Tt* — q — cqci o o qw o o vq — o o o 

w ’ ' ’ d — * * — 


VO 

O O On Tf 
VO co d ON 

o o 
d 


OOO 

O NtO 
to CN Cl 
• • • 
Cl 


oo^-o 

ci ci ci 
ON ^f N O 


o 

8 

Tf 


O VO O 
O vO VD 
O VO O 

d — 


ci O co O 
ci co co to 
q co cq — 

d ci - 


OO O O to 
M CO tON 
I-H CO Cl CO 

ri d h 


O O O 00 

O O Tf Tf 

to o oo o 
ci d 


o vo m o 
CO CO — vo 

O >—I HH HH 


vo O vo O H 

K CN O r^ O 

h h o o o 

d — 


O O vo O 

VO NO to 

to — o ci 
• • • • 
Cl M 


c0 

CO to 

*- 

CO 

CO Tf to 

* 

co 

CO Tf NO 

* 

• 

O Tf 

• 

Cl 

VO 

• 

0 

O 


O Tf- 


Cl 

to 


O 

O 

• 

O - 

• 

t-H 

Cl 

• 

vq t 

CO 


Tf vO 


HH - 

vd 


CO'* 

d 


Tf Cl 

• 

Ci 

ON 

• 

ON 

On 





00 


to 

CO 

. 

cd 

• 

Tf 


• 

Tf 








c 

< 

< 

< 

CO CO Tf to 

co 

Cl HH to 

CO 

Cl — to 

CO ci — 10 

CO ci w to • 

CO Tf H to 


* 


* * 


* * 

* * 

* * • 

* * 

• 0 

VO 

• 

ci 0 vo 

• 

OOO 

• O O O 

*H 

* O O O <-> 

• O O O 


On 


O 


OOO 

to O O 

0 o 0 p 

OOO 


Cl 

• 

Cl to ON 

• 

O O 

. ci ci 

• O CN Cl ^ 

. VO to ro 

VO ~ 

HH 


d cd d 


d dvd 

rded cd 

4 ^ CA " 

dv Tf\d 

. co 

HH 

• 

Cl ION 

• 

M COLO 

. co - 0 

. VD Tf M 

. CO ci 0 

VO 

to 


CO 1 ^. Tf 


ci 

vq Tf Tf 

Tf CO to fj 

vo ON to 

. Cl 


• 

d — 

• 

cd - 

. cd 

• 6 



OO 

Cl 


ON 

HH 

HH 

Tf 

HH 

t ^ 

HH 

0 

Cl 

i 

Cl 

Cl 

to 

Cl 

>> 

bb 

3 

bb 

0 

bb 

p 

bb 

p 

bb 

bb 

p 


bb 

p 

bb 

p 


F*' 

< 

< 

< 

< 

< 

< 


< 

< 




















































Analyses -arranged by days. TABLE C. ( concluded) 




62 


O 

o 

o 


P 4 

w 

C. 


co 

H 

< 

CL, 


* 


<D 


C3 




S M 73 G 


• ^ 73 3 • 

rt rt O P 


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< £ 5 i 0 « 


CJ 


bfl 73 7 ) 

g.SrS S 

.5 a <u o 

<- ^ 
a«.£ n 


c 

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fcjQ 

>> 

X 

o 


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> 2 

3 


o 

73 

73 03 
• - 73 


I 

C <u 
O c 
O p 
73 


<U 


JO 

<—' 

u 


a 

a; 

W) 

o 

u, 


a 


03 


o 

6 

S 

< 


TABLE C. 


O 


CM 


ON 

vq 

d- 

vo 


<x>N< 


coH< 


10(00 


r-trt 


H(N 


H|N 


CM 


00 

vd 

VO 


ON 


ON 


o 

o 


Tt" 

vd 

00 


o 

06 

VO 



£ 

0 






CO 


0 


0 


CO vo 

co 0 

On 00 

w 

*T-« 

co co 

CM 


CO 

ON CO 

Gn 


<L) <D 

vd ro 


vd 

COCO 

ONVO 

r^-vd 

vd rf 

d vd 

> 

O 

£ « 

P 3 

f 1 & 

CN ON 

ON 

ON 

On ON 

On On 

On vo 


a> 

















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£ 









O 

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MH • 

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V, w) 

a) as 
c_*> 





0 0 CO 



C 3 

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06 r^\d 

vo q 
*-* 06 

cn q 

VOX) 

GN CM ^ 

CM ON d 

VO 10 O 

^tzo on 

n rt q 

On Gn cq 
d- 4 VO 

Li 

3 

Cu 

1« 

•—C 73 

U 

GN GN 

VO ON 

rj- GN 

vo r^oo 

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Tf GN ON 

tJ* ONts 


OJ 









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8 8 £ 8 

CO 


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on 6 


rv.co 


88g? 

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o 

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vd ci 

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O O O VO 

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• • • • 
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10 


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rt *sf Xf 


O O CM CO 
COCO COCO 


CO hh 


1-0 CM 


VO HH 


f 2 o o o 

w . CM VOVO 
CO * 

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O O 

00 CO 


O 00 

t^co 


O O Tt- CM 
CO vOCO CM 


VO CM 


iO CM ►_ 


OOOO 
VO O CM O 


Cl 


On 

CM *-H 


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*0 o o 

6 ONvo 


8 


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0000 
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CO H M W 


O O O vo 
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8 


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VOVO CM o 
M 't M- 


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VO o O VO 

m 


GO 


vo 


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CO 


o 


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Cl CM 


o 

ci cm 


CM CM 


o 

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cm 

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O CO o 
O O Tf 


Tf CM 

o o ~ 
0000 


00 

OOO 

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O O h On 
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8 


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0 

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O 

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O OVO 

O 

O O 

O ^too CO 

O VO O vD 

O T}- Tf CO 

CM CM O ON 0 


co 

O 

vo 

Cl GN ^O 

O 

Tf- 

CO 0 

O vo Tf CM 

O ON VOVO 

O ir N CM 

5 

q 

CM 

• 

O O 

O ~ O 

HH 

CO O 
• • 

q h 0 h 

^ cm q q 

q co q q 

O cqo « 


HH 



t—1 

H-< 



CM 




8 8 2 8 
vo O O O 
• • • • 
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V 

a? 
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c 3 g: 
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73 W H IT) 

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v-.p a « 

<U 73 fC 7) 

— C 


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p 

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rt rt as 
P4 rt ° M 

<M 


•000 

coo 

. VO CO CM 


VO coco 
. CO CM Cl 
rv. GN GN 

. d“ 


O vo vo 

Cl 

- 0 

O 

r^vo vo 

CO ^ ^ 

Cl 

1— >—< 

O VO co co 

cq cq O 

Cl 

O 

r^vo O ^ 

CM »-« 

CM 


CM 


< 


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CO CM HH 

CO 

CM m 

CO 

Tt w vo 

* 


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• 0 0 


CO O 

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OOO 

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CO Cl 

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COOO N 

d »d 


VD On 


Gn ** vD 

• -tvD 

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CM °0 


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Cl 


O O Tf Tf 
00 CM CM M 

CO co O O 
ci h ’ * 


CM 


O vo o 

Tt" <o *—> 

VO vo O O 


88 

O 


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O O vo 


CM HH 


< 

C/} CO w vo 
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in co *-h vo 
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CO co ^ vo 

* * 


OOO 
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cocr CM 

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VO Tf vo 

^ #s 


Th O O 

On O O 

vo On 00 

^ #\ 

Cl GN 

VO H M 
t^OO 
CO •-» 


<D 


CTj 


vo O O 
O O 
Gn vo CO 


cJ 

P4 


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•- vo 
CO GNVO 


CO 


<u 

ri 

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vo 


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4 —> 


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Cl. 

O 

<D 

<u 

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CO 

CO 


r> 

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co 


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1-4 

CM 

4~> 

4-J 

4-j 


Q ( 

CX 

OJ 

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0) 

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CO 

CO 


























































TABLE C. 


6 3 








VO 


vo 







VO 


ON 







cd 


Ns 









CO 

d 

Cl 

HCl 

HH 


HrfJ 

VO 

Tf 

cow» 

co 

• 



Ns 








vo 


O 




d 

00 

cd 

GN 

001 

cd 

vo 

o 

CO 

cd 

Ns 

001 

Ns 

Tj" 

NO 

GN 


Ns NO 

O H« 

d Tf 

nh ro 

Ns GN 

00 Tt" rf* 

CO o 

O nh 

N 

q CO 

d d 

t-s vo 

Tf VO 

00 00 vo 

cq Ns 

rj-vq 

^TNO 

NO Ns 

Tf- Ns 

O d - 

ci d- 

vd Ns ci 

vdvd 

NO o 

GN GN 

ON GN 

GN GN 

GN GN 

GN ON 

d CN GN 

GN GN 

GN GN 


o 

Gn Ns 

M LO vo 

vq q- cq 

NO t-H d 

o 

o h vo 

q cq ON cq 

o Nq 

cq cq o 

o 

NsCO 

GNvd Ns 

Ns NO cd 

O cdvo 

cd vd\d 

od vd 

hn* NsCO 

ci NsOO 

NO 

GN ON 

ON GN 

CO GN GN 

CO GN gn 

co On GN 

co vo GN GN 

vo Gn GN 

n - GN on 



Ns 0\ 

co o 

CO gn 


O O O ~ NO co 

O ^ r-s, vo O'* 

CN ON CO ON 


O - Tf vo 
0 ~ rj-ci 
CO ON 


no h vo 

d° nn 

ON GN 


CO VO 

tt o 
CO ON 


'to O W 

cd ° cd GN 
hh CO CO 


NOVO O 
CO° H N 
hh GNCO 


O O 00 Cl 

O ONo 


O O O 

o 

O O Cl 

o 

o 

d 


o 

• 

O NO 

Cl 

o 

O CO 

d 

O O rN O 

vo Ns Tt- 

HH NH 

vo 

O NO vo t}“ 

00 

LONG vo 

»—i 

vovO 

q - 

GN 

• 

ON vo LO 

co o 

Cl 

q* 

vo t-. vo vo 

Ns HH 

cd ci 



d- d 

ci 

HH 

co hh 



cd 

• 



d 

H- 



ci HH 

o o o o 

o o 

o 

o 

O O O O 

o 

o o o 

o 

O 

o 

o 

o 

• 

o o 

O 

o 

o 

o 

o 

O O O O 

LO LO VO LO 

VO vo o 

LO 

LO O vo vo 

o 

vo o vo 

vo o 

vo vo 

vo 


O vo LO 

c 

o 

vo O 

vo O O O 

>0 on co cd 

NO O 

o 

Gn 

cd ci cd cd 

NiOCOi* 

H-* 

d 

HH 

Cl 

H— 


On Gn Gn 

Ns. 

t—1 

cd o 

Gn GN O O 

Hh NH *-H 

NH NH 

HH 


Cl co Cl Cl 

hh 

ci d d 

HH 


t-H 

NH 

d 




t-H 

HH 

Cl 

Cl 

NH t-H 

• • 

• • 



• • 

• 

• 

• 

• 



• 

• 

• 



• 



• • 

* * o o 

• • 

o 

O 

• • 

O O 

• 

o o 

• 

• 

o 

o 

• 

• 

• 

o 

O 

o 

• 

o 

O 

o o 

• • NO 

• • 

d 

O 

• • Tf- t}- 

• 

• VO Tj- 

• 


NO 

o 


• 

• Cl 

q* 

t-H 

• 

o 

Cl 

* • O CO 

• • HH HH 

• • 

HH 

HH 

• • *—i »—i 

• 

* HH HH 

• 

o 

l-« 

NH 

• 

• 

• t-H 

t-H 




t-H 

• • t-H 

. q-NO CO 

• 


VO 

d ^fco 



• 



Cl 



co ^ 


o 

Ns 


. CO vo d 

o o o 

o 

o 


O O w 

o 

o o o 


o 

o 

o 

o 

o 

O d 

o 

o 

o 

o 

O 

t— NH NH 

• o o o 

• • • 

• 

• o 

• 

o 

O 

• 

o o o o 

o 

o o o 

• 

o 

o 

o 

• 

o 

o 

° 9 

o 

o 

t-H 

o 

O 

• o o o 

• • 4 

• 


O O CO ON 
ON ^ ^ n 
t—< ci O O 


o oco n 

d vo CO 
^•M O O 


0 0^-0 
't oco ^t 
M COO O 


o O NO NO 

Tf NsCO 

VOW o O 


O O NO cj 
rf VON ^ 

VO W O O 


O VO O CO 'O 
H CO N 
CO Tf co o o 


O NO *-* C l 
O GN CO d 
Ns t-. <3 O 


O O ci O 

VO Tf CO 
00 Cl O O 


O NO NO 

_ Ns o o 

vOtTO O 

ci 


88 


Ns NO 

o o 

w Cl O O 
ci ci 


< < 

C n Cl VO) NH CO Cl VO) t-< 

* * * * 


oco 

o o o 

Ns Ns Cl 

#s rs *\ 

co ci Ns 
VO NO CO 
CO d 

lO) hh 


• o o o 
o o o 

.W NH 

r» ^ 

co *- ci 

. H Cl Ns 

O vO) CO 

rv 

. CO 


O O d NO 
0 0^0 
VO) lo O O 

ci ci 


< 

CO ci vo >—< 
* * 


• O O co 

GN O Ns 
. H 00 Cl 

#*V #s 

Tf- O 
. VO) co 

O vo Cl 

rs 

. d hh 


O O vovO 
O vo o o 

vo d O O 
• • • • 


< 

C/3 TflOH 
* * 


•VO TfM 

co q- rr 

. CO NsVO 
co" CO NO 

• Cl CO 

N w lO 

. d 


O O Tt-co d O O Tt-CO o O co ci o O Cl ci 

O N. O ci dVO h O ^ ^fOOO OOOd 

on vo o o m vo h q o tt o o o voqqo 

HH HH Cl HH t—I HH hH d Cl 


< 

CO Tf VO t-H 
* * 

< 

CO CO Tt" VO HH 
* * 

< 

CO CO VO hh 

*- * 

< 

CO CO VO HH 

* ^ 

• o o o 

• o 

O O 

• O O O 

• Tt O NO 

o o o 

O 

o o 

O O O 

00 O Ns 

. ON Cn 

. co 

CO GN 

• GN Ns Ns 

• CO ON Ns 

t-T cd *d 

co - 

Gn 6 

N N Ns 

od on cd 

- NO ON 00 

. CN 

Ns GN 

. NH O 

. Ns LO co 

O vo co 

Cl 

d vo 

q VON 

o nh 

. cd 

. cd 

Hn HH 

. d 

. Tf Hh 


CO 

NO 

00 

CO 

d 

Cl 

Cl 


• 

• 

4 H 

4 -j 

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r>, 

<u 

CO 

n, 

G 

CO 

p 

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CO 

Oct 


vO 

00 

HH 

co 



HH 

HH 

• 

4 -* 

4 -j 

4 ~j 

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CJ 

G 

G 

O 

o 

O 

O 



































TABLE D 


Q 

W 

PQ 

< 

H 


O 

o 

o 

o 

o 


w 

p* 


CO 

H 

< 

P-i 


CO 

Ph 

W 

£ 
»—i 

< 

P$ 

H 

C/3 

O 

< 

►—< 

P$ 

w 

H 


O 

►—< 
P 4 

w 

P5 

Q 

W 

K 

p$ 

w 

H 

H 

<! 

S 

fa 

O 

55 

O 
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H 

£ 
H-< 

s 

fa 

w 

H 

w 

Q 

< 

*—< 

a 

o 

S 

<3 

55 

O 

ID 

o 

P 4 























TABLE E. — SUMMARY OF RESULTS. 


TABLE E 


65 


CO 

C N 1J 

£ ^ 

«-» "''v fu 

c\^ 

U ^ 

c V > 
o 

2 S * 

sg§ 

to ^ • — 

<u ~ 

v- -3 -r* 

►■*•• »—« r\ 

S £ 

3 <L> W 

cpT cS O 

K £ C 

Sd 2*S 

^ 3 <-> 
.5 ^ ^5 
c o*c 
o o 3 

|c & 

CWr-r 


o2 . 

•£ ^3 

. O q_) 

to ~ > 

CO 

<D <D <L> 

y 

C W (D 
i- s-. 
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0 « 

<4=7: >- 8 

,2-SS 


T5 

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<L> G 
tJO C ^ 


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rt ^ 


03 


rt ^ ^ 

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te «* 
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to •—' 
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<1>L-| <L 
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rJ'O J W) 

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J ^.S 
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E .2 



* These figures are necessarily only approximate, as they represent not only the sewage actually filling the tank up to the overflow pipe, 
but also that retained in inner compartment by the frictional resistance at time of draining. The error, however, is small. 







































































66 


TABLE E. 


•§ 


w 

w 

cq 

< 

H 



* 

































































TANK No. 5. 

(Aerator.) Filled with fine beach gravel. Filtering surface = rsW °f acre. Voids of gravels after draining = 34.4 %. No. 


TABLE E 


67 


O t^vo ro\Q 
'pvd ONO 
Cl '-O'O ON 


o no 
no >-d 

CO GO 


nJ- O r^. o “N't 
fdoo cd no conO 
O VO CO On On On 


h O N 10 Tj-—'— ri- 

w NO °°. ^ « CO 
no r^co On On h co On On 
On On 


NO fONO w ON 
no cd cd rdvd d. 
ONCO On On ON On 


VO 

HH 


NO 


00 


<D 





C 

15 

( 

/^N 

C/2 


3 

CJ 

0 

CS 

CJ 

^-> 

cC 

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C/2 

a 

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0 


HH 

2\l fi 



>-1 


t^ 

to 55 

-*-> 

ci 


O, 

£ 


<u 

in 




fci 


OOOOOOOOOOOOOOOnonn 

qooooooooooooooooon 
o o. qqqqqqoooooooooo 

LO On NO nooO CO rp ~ k H o' o' N d LOCO rC id n 
5 N OnnO CO LO co O CO CO rroo to « cTc>o 

On lo On OnnO CO CO ro M-vO NO no conO No t^vo To 
cd cd« cT d 


00000000000 
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o o o o o o o_ 
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o noO tJ-nO O no conO h Cl 
LqoqNrq^q.Tj-„oq_ coco 
NoidoNTpcTcd cd On cT 
CO >-1 *1 


00000 
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co N NO vo NO Tp 


O O 
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1-1 10 

cd w 


r-tMi-H*i-H<ech7<cc|oor-i|ooi>|» HooH°°H»H im mW<coN«»H< 
•—II—11—II—11—11—11—1 


^ •nj- ^ 


O fj On co O q.cq go ^ On q- Tt o no q- noco no 
tP ci cd On rdvd cd On d id no dcioO d»o On On On 
r^-vo 00 co On 10 rooO t^co >oionnn c^no no 


O ono o coq o d 1 "O h itHoooq co 
ci no cd Nordd-^Ndd rdcd vd cd cd On-^i-i cd ci 

ON OnvO 00 n(- m ro't •cTnO vf Cl i-i rf Tf IOON 

■^J-NO CON N N CO'O I- ci - *cf“ NO NO NO NOvO MO N 

00 cd o' cT w ON cT ^ NO cT hT h hT cd cd cT N hT 


NO o ONO hi ON CO ON CO fO N ►- 
O CO i-iwOOi— 1 O 1 - 1 OO NON 


Cl d 00 fOK 

d h hi 


to 

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1 tjO 

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w N M h N N H COH N N h Cl Hi 


to 

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